This application claims the priority of German patent document 102006004517.3-15, filed Feb. 1, 2006, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and an apparatus for defense against missiles that have explosive substances with piezoelectric detonators.
Piezoelectric sensors are frequently used as percussion detonators for triggering explosive payloads in unguided missiles, (for example, rockets or shells). One such missile is the Russian RPG-7 anti-tank grenade, shown in FIG. 1.
This weapon, which is widely used, is responsible for a large number of casualties in the present-day asymmetrical war scenarios. The main defense against such weapons is armor. However, armor is not always effective against the powerful plasma beam generated by a shaped charge.
Active defense systems that attempt to shoot down the missile in flight have been proposed. These are, however, very expensive, have only a low hit probability, and cannot be used where the missile is launched close to the target. Defense systems based on microwave energy are not suitable because the rocket housing forms a shield against the electromagnetic radiation that can be overcome only by extreme power levels.
German patent document DE 22 50 630 B2 discloses a remote triggering systems that uses ultrasonic signals to detonate explosive charges underwater. An ultrasonic receiver, which is assigned to an explosive charge, receives the ultrasonic signal, converts it to an electrical signal and subjects it to further processing. The output signal of the ultrasonic receiver is applied to an electrical detonator to trigger the detonation.
One object of the present invention is to provide a method and a system that enables a very reliable defense against missiles.
These and other objects and advantages are achieved by the method and apparatus according to the invention, in which ultrasonic radiation is emitted to counter the incoming missile. Such radiation causes the piezoelectric detonator of the incoming missile to oscillate and thus triggers the detonator that was activated after the launch of the missile. The explosive payload is thus triggered far from the target during the approach of the missile.
The emitted ultrasonic radiation, which can be directed or undirected can penetrate the metal casing of the missile with only slight attenuation. Directed emission of ultrasonic energy is preferably in the form of a high-energy beam with a small angle of aperture. For this purpose, an array of several ultrasonic transducers is preferred, which permits the emitted energy to be aligned by appropriate phase control of the signals of the individual ultrasonic transducers (phased-array technique). Alignment is therefore by purely electronic means without moving mechanical parts.
Alternatively, however, mechanical control of the alignment, such as is used with radar systems, can be provided. For example, the ultrasonic generator may be mounted on a turntable that can be adjusted in azimuth and elevation.
A combination of electronic and mechanical alignment is also possible. For example, a turntable may be used for the azimuth alignment, while alignment in elevation is carried out electronically by means of an array (or in its simplest form by means of a line) of ultrasonic generators.
The frequency of the ultrasonic radiation is preferably chosen so that the piezoelectric detonator of the incoming missile is excited at its natural resonant frequency or a harmonic or subharmonic thereof.
To compensate for tolerances in the known resonant frequency of the detonator or uncertainties with regard to the precise value of the resonant frequency of the detonator, the emitted ultrasonic frequency can be varied over a certain frequency range, e.g., by linear frequency modulation.
Furthermore the Doppler shift that occurs due to the relative speeds of the missile and the platform transmitting the ultrasonic radiation can also be advantageously taken into account in the choice of emitted ultrasonic frequency. Also in this connection, the frequency of the ultrasonic radiation can be varied to compensate for uncertainties with respect to the exact value of the Doppler frequency.
With the method according to the invention, a reliable and cost-effective defense against missiles is realized. Direct hits by the missiles, and thus the formation of destructive plasma jets in the direct vicinity of the target, can be avoided.
The method according to the invention is suitable for defense against all guided and unguided missiles, e.g., rockets or shells.
A system for implementing the method according to the invention includes the following main components.
a) A missile warning sensor for detecting the launch of the enemy missile. Known missile warning sensors based on IR, UV or radar sensors can be used for this purpose. The software of the warning sensor is advantageously tuned to the specific signature of the relevant missile.
b) A tracking sensor for tracking the incoming missile. This may be either the same sensor as the missile warning sensor or an additional sensor. For instance, a passive electro-optical sensor based on a UV sensor can be used. Because of the limited burn time of the missile, the use of an IR sensor is preferred. An active radar sensor is quite particularly suitable because the method according to the invention can be most effectively implemented on the basis of range information.
c) A positioning device or aligning the ultrasonic beam on the incoming missile. The alignment takes place in such a way that the travel time of the ultrasonic beam to the target is allowed for.
A rotating turntable that enables the radiation to be mechanically set in azimuth and elevation can be used for this purpose, for example. The alignment can also take place by purely electronic means in that the phases of the individual ultrasonic generators of a two-dimensional array are suitably controlled. Electronically controlled acoustic arrays such as are known for example from sonar systems for underwater applications can be used for this purpose.
d) A device for generating ultrasonic waves. Devices that are suitable for generating a high-energy, narrowly focused ultrasonic beam with a high energy density are preferred for this purpose. Two-dimensional arrays consisting of single acoustic radiators are especially suited to this purpose. Their frequency is, for example, set to the resonant frequency of the piezoelectric detonator of the RPG-7 anti-tank grenade. The alignment of the emitted ultrasonic energy in azimuth and elevation takes place (as already explained in item (c) above, electronically or mechanically, or by a combination of electronic and mechanical means.
The described method can be carried on aircraft or on land vehicles. Stationary on-ground applications are also possible. A particular advantage of the system according to the invention is its very short reaction time, which is particularly important when under close-range bombardment.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.